This invention relates to the field of manufacturing electro-mechanical systems which includes nano-electro-mechanical systems (NEMS) and micro-electro mechanical systems (MEMS). More particularly the invention relates methods of making MEMS and NEMS using vapor hydrofluoric etching.
NEMS are modern mechanical systems in which one of more of the mechanical elements are smaller than one micron in all directions. NEMS and the older technology MEMS are well known devices which consist of long thin beams that support large plates, all patterned on top of a sacrificial layer and anchored to the underlying substrate at one or more points. After the device is completed, the sacrificial layer is etched away and the plate and beams are free to move except at the anchor points.
Many patents and other publications disclose various methods of making NEMS and MEMS. For example, Mastrangelo U.S. Pat. No. 5,258,097 disclosed a method of fabricating microstructures on a silicon substrate by depositing a sacrificial layer which can be removed by wet etching techniques such as silicon dioxide. Void areas are formed in the sacrificial layer and then a column-forming layer, resistant to sacrificial layer etchant, is deposited through at least one hole to fill the void area and undercut areas which later provides support for the structural layer during wet etching of the remaining sacrificial layer.
Others have addressed problems associated with NEMS which were not associated with MEMS, for example Carley, U.S. Pat. Pub. 2010/0061143, addressed the problem of constructing beams which have small aspect ratios by constructing them as independent, unattached objects. Rueckes, et al, U.S. Pat. No. 6,911,682, addressed the problem of controlling the statistical variance of geometries of nanotube wires or ribbons grown for memory cells. Beyer et al, U.S. Pat. No. 7,078,352, addressed the problem of isolation between interconnect lines by using air cavities which use hydrofluoric acid (HF) to dissolve sacrificial a SiO2 layer by etching a hole and depositing an electroconductive material in the hole.